Validation of a very simple model for computing global solar radiation in the European, African, Asian and North American areas

In a previous paper Coppolino has proposed a very simple model for predicting the monthly mean daily global solar radiation G(MJm⁻² day⁻¹) at any Italian location using as input only the sunshine duration s (hours) and the noon altitude of the sun on the 15th of the month h_n (degrees). The correlation suggested is G = 7.8s^0.5(sin h_n)^1.15. Herein the validity of this model is verified by extending its application to dat from 24 stations displaced at various latitudes, altitudes above sea level and geographical situations in the European, African, Asian and North American areas. Furthermore the validity of this model to fit the data of the tested stations is compared with that of the well-known linear Ångström equation. The test results show that: (a) The correlation proposed by Coppolino fits well enough the measured data of the monthly mean daily global radiation for all tested stations, independent of their latitude, altitude above sea level, meteorological conditions and geographical situation (inland or coastal site). In fact the related standard per cent error of estimate Φ(%) is less than 10% for all tested locationswith the exception of Goose Bay, Canada, for which it is a little higher than 10%. (b) Although the values of the regression constants of the Ångström equation vary from location to location and for some locations from north to month, the values of Φ(%) referring to the two compared correlations are nearly equal to each other for each station considered. Consequently it must be deduced that the very simple model suggested by Coppolino is suitable and useful to predict the monthly mean daily global solar radiation with good reliability, even in the locations of the European, African, Asian and North American areas lacking actinometric instruments but provided with sunshine duration data.